Industrial fluid delivery systems routinely include one or more fluid valves configured to control the rate of, or completely terminate, fluid flow through the system. One type of valve commonly employed to control the flow of fluids in a fluid delivery system is a ball valve. A conventional ball valve generally includes a valve body having a fluid passageway therethrough. A ball or ball element is positioned within the valve body so as to be placed in the fluid passageway. The ball in a conventional ball valve has its own fluid conduit extending therethrough and defining a flow path through the ball. When the conduit in the ball is aligned with the fluid passageway through the valve body, fluid may flow through the valve generally unimpeded. If the ball is rotated such that the ball conduit is out of alignment with the valve body passageway, then the flow is restricted.
The ball is contained within the valve body between two valve seats with physical compression applied to the seats during assembly, such that the seats bear into the ball with force. In such designs, the valve seats act as a seal at the point at which they bear onto the ball, and as a seal at points at which they bear against the valve body. The valve seats also act as a spring to maintain the sealing force during operation of the valve. The “off” position usually corresponds to a position of the ball wherein the conduit is at right angles to the valve body passageway. However, lesser angular displacements may result in an “off” or partially “off” condition, depending upon the geometry of the valve components. The full “on” position is typified by the ball conduit being coaxially aligned with the fluid passageway of the valve body. A conventional ball valve provides varying degrees of flow restriction based upon the degree of alignment of the ball conduit with the valve body passageway. Thus, for a given pressure, flow is controlled by varying the degree of alignment of the ball conduit with the valve body passageway.
A ball valve is usually actuated or rotated through a stem which passes through the valve body and attaches to the ball. A handle or some other means, such as a gear, may be attached to the opposite end of the stem in order to turn the stem. The amount of fluid passing through the ball valve changes as the ball rotates. A particular angular orientation of the ball corresponds to a particular degree of alignment between the conduit and the passageway, which in turn corresponds to the flow rate.
During the life of the ball valve, switching the ball between the “on” and “off” positions subjects the valve seats to thermal cycling, which can damage the valve seats and cause the seats to experience “creep,” which degrades the seal and causes leakage within the ball valve assembly. Valve seats made of softer, more elastic materials require less compressive force to seal the ball; however, such softer, more elastic materials are more susceptible to creep, which may occur rapidly at elevated temperatures. To compensate, valve seats are often configured to provide a maximum physical compression against the ball, wherein the sealing force may be maintained even if some thermal degradation or creep occurs. However, such compressive forces require more torque to operate the ball valve.